[FC-0006] feat: Add settings for Verifiable Credentials

[GlugovGrGlib]

This changes allow to configure Verifiable Credentials settings for the "credentials" service.

Related PR:
openedx/credentials#1973

Configuration Pull Request

Make sure that the following steps are done before merging:

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• Are you adding any new default values that need to be overridden when this change goes live? If so:
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• If you are making a complicated change, have you performed the proper testing specified on the Ops Ansible Testing Checklist? Adding a new variable does not require the full list (although testing on a sandbox is a great idea to ensure it links with your downstream code changes).
• Think about how this change will affect Open edX operators. Have you updated the wiki page for the next Open edX release?

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[adzuci]

Could these todos be cleaned up?

[GlugovGrGlib]

Thank you, resolved

The link to VC documentation was added. It's 404 as for now only because the documentation PR is still in review openedx/credentials#1991

[justinhynes]

I think this LGTM. I was able to pull these changes into a branch and deploy an internal sandbox with the changes, which I believe still use ansible. The service was deployed and functional. 👍

[e0d]

@adzuci would you like to merge this or should I?

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